Conventionally, a chemical vapor-phase epitaxy method, such as a plasma CVD method, a photo CVD method, or the like, using a gas such as a hydrocarbon gas or an organic compound series gas has been employed as a means for forming or synthesizing a diamond thin film of a substrate.
In conventional methods, however, the following problems have been observed:
(1) Simultaneously with the crystal growth of diamond, deposition of graphite is generated when using a hydrocarbon gas or an organic compound series gas;
(2) It is necessary to treat the substrate and a gas atmosphere at a high temperature (for example, about 800.degree. C.-1000.degree. C.), so that the material which can be used as the substrate is extremely limited; and
(3) When the substrate has a large area or a complicated shape, the flow of the reaction gas tends to become uneven, so that a diamond film can not be formed uniformly on the substrate.
It is therefore an object of the present invention to provide a method of forming a diamond thin film in which the above problems in the prior art are solved.